A variety of manufacturing machines use a beam of radiation for performing a portion of a manufacturing process. For example, lasers or electron beams are used for achieving desired surface finishes. Other machines use lasers or electron beams for producing three-dimensional products by successively fusing together layers of powder. Such powder bed additive manufacturing machines are used for a variety of purposes.
One shortcoming of known surface finishing or powder bed additive machines is that it is difficult to apply the laser or electron beam over a large surface area. It is difficult to achieve a desired angle of incidence for the laser or electron beam across a larger surface area. Some proposals to address this situation include using multiple lasers or mounting a laser on a gantry so that it is moveable relative to the work surface. For machines that include electron beams, this is more difficult because they require a vacuum and there are practical limitations on how large a vacuum chamber can be made.